The correct answer is (a) Silicon.
Silicon is a semiconductor, which means that it can conduct electricity under certain conditions. This makes it ideal for use in computer chips, which are essentially tiny electronic circuits.
Carbon is also a semiconductor, but it is not as widely used in computer chips as silicon. This is because silicon is more abundant and easier to work with.
Iron and uranium are not semiconductors and are not used in computer chips. Iron is a metal that is used in many different applications, including construction and manufacturing. Uranium is a radioactive element that is used in nuclear power plants.
In conclusion, the primary element used in computer chips is silicon. Silicon is a semiconductor that is abundant, easy to work with, and has the properties necessary for use in computer chips.